Proceedings of Topical Meeting on Optoinformatics (pdf-format, 1.21 ...

SAINT-PETERSBURG, October 17 – 20, 2005 41
CdF 2 :In: A FAST-RESPONSE MEDIUM OF THE REAL-TIME
HOLOGRAPHY
A.E. Angervaks, S.A. Dimakov * , S.I. Kliment’ev * , A.S. Shcheulin, A.I Ryskin
S.I. Vavilov State Optical Institute, 199034 12, Birghevaya Line, Saint-Petersburg, Russia
* Institute for Laser Physics, 199034 12, Birghevaya Line, Saint-Petersburg, Russia
E-mail: angervax@mail.ru
Opportunities <strong>of</strong> use semiconductor CdF 2 crystals with bistable indium centers
as a high-frequency medium <strong>of</strong> the real-time holography is discussed.
Indium ions in semiconductor CdF 2 crystals form bistable centers having two states,
ground (the “deep”) state and excited (the “shallow”) state. Two states <strong>of</strong> the center are
separated with a potential barrier, due to which the excited state has a metastable nature.
The strong photoionization absorption band is tied with each <strong>of</strong> two center states: in the
ultraviolet-visible (UV-VIS) range <strong>of</strong> the spectrum for the deep state and in the infrared
(IR) range for the shallow state. These bands are due to electron transfer from the
corresponding center state to conduction band <strong>of</strong> the crystal. The photoinduced conversion
<strong>of</strong> the deep centers into the shallow centers correspond to transforming an electron from
the tightly bound into weakly bound state with corresponding change <strong>of</strong> absorption
spectrum and refractive index <strong>of</strong> the crystal. This conversion underlies the process <strong>of</strong>
hologram writing in the crystals with bistable centers [1,2] . The hologram decay is due to the
thermoinduced conversion <strong>of</strong> the shallow centers into the deep centers. Because <strong>of</strong> the
small height <strong>of</strong> the barrier the decay time is very short: at room temperature it is <strong>of</strong> ~ 10 -7 s.
Due to this dynamical holograms written in CdF 2 :In, crystal can follow processes with
frequency up to ~ 10 MHz [3,4] .
High spatial resolution (> 5000 lines/mm), cubic symmetry <strong>of</strong> the crystal,
unrestricted number <strong>of</strong> writing/reading cycles, and opportunity <strong>of</strong> growing crystals <strong>of</strong> large
dimensions and good optical quality make CdF 2 :In a promising medium <strong>of</strong> the real-time
holography.
One may show two fields <strong>of</strong> using this medium. The first one is dynamical
holographic correction <strong>of</strong> the optical image. The CdF 2 :In-based dynamical PC mirror used
for this purpose ensures response time about 15 ns at reflection coefficient up to 2%. The
gain in the beam divergence at compensation <strong>of</strong> model large-scale distortions is 20 times at
the quality <strong>of</strong> compensation <strong>of</strong> 1.05 [5] .
CdF 2 :In crystal with renewed holograms can also be used as a dynamical holographic
filter in problems <strong>of</strong> the image recognition and optical processing <strong>of</strong> information. In the
model experiment comparison <strong>of</strong> two transparencies has been executed during the 20 ns
pulse <strong>of</strong> YAG:Nd laser [6] .
1. R.A. Linke et al., Appl. Phys. Lett., 65, №1, 16-19, (1994).
2. A.I. Ryskin et al., Appl. Phys. Lett., 67, №1, 31-33, (1995).
3. S.A. Kazanskii et al., Physica B, 308-310, 1035-1037, (2001).
4. A.S. Shcheulin et al., Opt. and Spectr., 92, №1, 133-141, (2002).
5. A.E. Angervaks et al., Opt. and Spectr., in press.
6. A.S. Shcheulin et al., Opt. and Spectr., in press.